Tanning agent and process



United States Patent TANNING AGENT AND PROCESS No Drawing. Application July 13, 1954, Serial No. 443,180

(Granted under Title 35, U. S. Code (1952), sec. 266) Claims.

A nonexclusive, irrevocable, royalty-free license in the invention herein described, for all governmental purposes, throughout the world, with power to grant sublicenses for such purposes is hereby granted to the Government of the United States of America.

This invention relates to the tanning of hides and skins and to the leather thus produced.

An object of this invention is to provide novel tanning materials and processes. Another object is to provide leather having new and improved properties; in particular, leather that retains leatherlike properties after being heated above its shrink temperature and that shrinks reversibly when so heated.

The shrink temperature of leather is intimately related to the type and degree of tannage used in its preparation. Untanned hides have a very low shrink temperature (about 60 C.) and, when heated at or above this temperature in the presence of water, shrinks irreversibly to yield on drying a hard, horny, translucent product having no resemblance to leather. Conventional tannage yields leather of somewhat elevated shrink temperature. If heated above such temperature, however, it shrinks irreversibly and becomes hard and stiff, thus becoming useless for most applications.

According to the invention, a new type of leather is made by applying a tanning composition containing as the tanning agent a polyglycide ether of glycerol, preferably in aqueous suspension, to hides and skins or pretanned leather until they are termed. These tanning agents are conveniently made by condensing epichlorohydrin with glycerol according to well known procedures such as, for instance, that described in U. S. Patent 2,521,912, and are believed to be of the following structure:

materials are complex mixtures and can only be represented by their average composition. Since glycerol is tri- "functional it can react with three moles of epichlorohydrin, thus giving rise to branched-chain or even crosslinked condensation products, in addition to the linear products represented by the above formula. It is believed that this actually occurs to a certain extent, either in the preparation of the polyglycide ether, or in the use of the latter as a tanning agent, or both, and that the -unique tannage achieved in the practice of the invention is directly related to this ability of the polyglycide ether 'to form branched and/or cross-linked chains. This view *is substantiated by the fact that, of the many monoand di-epoxides that have been used or suggested for use in tannage, none has been observed or reported to give the unique valuable properties achieved with the glycerol polyglycide ethers of this invention.

Hides, skins, or pretanned leather, afiter being tanned 2,795,478 Rptented June 11, 1957 with our polyglycide ethers of glycerol, not only shows the usual valuable properties imparted by conventional tannages but in addition show several distinctive new and useful properties. The most startling new property is the behavior of the leather when exposed to stea'm'or hot water. Ordinary vegetable-tanned leather has a characteristic shrink temperature of about C. and if heated above this point undergoes irreversible shrinkage such that after it is cooled and dried it is shrunken, warped and misshapen, and is also hardened, stiffened and embrittled so that it no longer has leatherlike properties. In contrast, when leather tanned by the process of this invention is heated above its shrink temperature, although it shrinks somewhat, the shrinkage is reversible and the article recovers substantially its original shape and dimensions upon being cooled. Of equal importance, it retains substantially its original shape, feel, flexibility and other useful properties. Another highly valuable property of leather tanned by our process is its ready wettability. In the commercial processing of hides, skins and leather occasions frequently arise where it is necessary to rewet them after they have been dried. Frequently such rewetting is a slow and tedious process and often the effectiveness of the subsequent treatment is impaired by the rewetting having been uneven or incomplete. We have found that hides, skins and leather treated by our process rewet with great speed and uniformity. Ere quently this ease of rewetting is a valuable property in the finished leather product, as in chamois leather for instance. Where it is objectionable it is easily counter acted by conventional treatment of the leather with oils, waxes or.other hydrophobic agents.

The practice of the invention is illustrated by the following examples.

Example I Pickled cowhide was depickled by a two-day immersion in 5% aqueous solution of sodium bicarbonate. After being rinsed with water, 15 g. (dry weight) of the wet hide was rolled in a jar mill together with a suspension of 10 g. of a glycerol polyglycide ether in 200 ml. of water. The polyglycide ether had an epoxide equivalent of about 150' and its average composition corresponded to the structural formulaabove wherein n has a value of about 2. After two days in the jar the pH of the liquid, originally 8.1, had dropped to 6.9. The hide was rinsed with water and its shrink temperature was determined. It shrank at 80 C. but even after heating in boiling water it regained its original dimensions on cooling. It was a firm light-colored, flexible, high-quality leather and showed no undesirable elfects from having been heated above its shrink temperature.

Example II A 20 g. (dry weight) sample of the wet depickled hide used in Example I was treated as in Example I with 10 g. of the same glycerol polyglycide ether in ml. of. water, the significant diiference being that a wetting agent was used (1 g. of sodium lauryl sulfate). After 24 hours in the jar mill the sample was removed, rinsed and evaluated. Its shrink temperature was 80 C. After 1 minute in boiling water it was cooled, whereupon it regained its original dimensions and appeared identical to the product of Example I.

Example III A sample of the depickled hide of Example I was dehydrated by immersion first in 50% aqueous acetone and then anhydrous acetone. The sample was then tanned by a 3-day immersion inv a 15% acetone solution of the glycerol polyglycide ether used in Example I.

After being rinsed with acetone and dried, the sample was wet back'with water. It was found to be distinctly 3 hydrophilic and was quickly and even wet by water. Its shrink temperature was 72 C. After being boiled in water for 1 minute and cooled it recovered its original dimensions.

Example IV A sample of pickled calfskin was tanned with the same glycerol polyglycide ether and the same procedure as in Example I except that the aqueous suspension of tanning agent contained of sodium chloride. The tanned leather had a shrink temperature of 73 C. The shrinkage caused by boiling in water for 1 minute was fully recovered on cooling and all characteristic leatherlike properties were retained aftersuch. treatment.

Example V A sample of the depickled cowhide used in Example I was relimed by soaking it for 24 hours in saturated lime water. The hide was then tanned as in Example I with substantially identical results as in Example I.

Example VI The effect of pH on the tanning process was studied by conducting a series of experiments similar to Example I except that various butter salts were used to adjust the pH.

The aqueous suspension of tanning agent was adjusted to pH values of 11.1, 9.1, and 4.6 by adding respectively sodium carbonate, sodium bicarbonate and potassium dihydrogen phosphate to make 0.2 molar solutions. After 24 hours in the jar mill the pH of the liquors were 10.4, 8.8 and 5.3 respectively. An additional 24 hours made no change in the pHs.

The shrink temperatures of the 3 samples of leather were 73", 78 and 72 C., respectively. All recovered fully from the shrinkage caused by boiling in water for 1 minute. In all respects other than the shrink temperature the 3 samples appeared identical, being light colored, firm, flexible, high quality leather.

Example VII Cowhide that had been tanned as described in Example I was retanned with a 50-50 mixture of chestnut extract and sulfited quebracho extract in aqueous solution in the conventional manner.

The retanned hide had a shrink temperature of 83 C. and the shrinkage caused by boiling in water for 1 minute was regained on cooling.

Example VIII A series of experiments was run to show the rate of tannage and the accompanying pH changes under various conditions.

Pickled calfskin was depickled by 24 hours immersion in 5% aqueous sodium bicarbonate. The skin was rinsed to remove salts and then 20 g. samples (dry weight) were put in jar mills with g. of the glycerol polyglycide other used in Experiment I and 100 ml. of water. Nothing else was added to one; 1 g. of sulfonated cod oil was added to the second. While 1.7 g. of sodium bicarbonate was added to the third.

At regular time intervals the pH of the liquor and the shrink temperature (Ts) was determined with the results shown in'the table below:

Expt. Reagent Added O 1... None 2 Sult'onnted cod oil.-. 3; Sodium bicarbonateso so I All the samples in the above experiments showed excellent tannage and all showed the reversible shrinkage when heated in boiling water that is characteristic of the invention.

Example IX A piece of depickled calfskin 2" x 4" was treated in the jar mill with a suspension of 5 g. of the glycerol polyglycide ether used in Experiment I in 100 ml. of water containing 1 g. of calcium hydroxide. The pH was 12.4 and remained substantially constant throughout the experiment.

After 4 hours the shrink temperature had risen from the initial value of 60 to 71 C.; after 8 hours it was 76 and after 32 hours it was 80. Longer treatment caused no further change. The 4 and 8 hour samples showed excellent leatherlike properties and recovered almost their original dimensions after being boiled in water for 1 minute. The 32 hour sample was completely tanned and showed substantially full recovery from heat shrinkage without any apparent loss of its leatherlike properties.

While in the above examples the tanning agent used was a glycerol polyglycide ether having an average composition corresponding to the formula shown above wherein the value of n was about 2, similar results are obtained by the use of similar glycerol polyglycide ethers wherein the value of n is in the range of about 1 to 6. Lower values yield leather that is somewhat harder and stiffer than is usually desired, while ethers in which the value of n exceeds about six have physical properties such that tannage is unduly slow, presumably due to the slow penetration of the tanning agent. Leather tanned according to the invention is suitable for use with all the conventional finishing agents and processes.

The process of the invention is applicable not only to cowhide and calfskin, as described in the above examples, but also to any hide or skin commonly used for tannage except the fur skins. The term hide as used in the claims includes all such hides and skins.

We claim:

1. A process of tanning hides comprising applying to the hides a tanning composition containing as the tanning agent a glycerol polyglycide ether corresponding to the formula CHr-CH-GHr-O-[CHz-CHOHCH2O]CHzOHCHr 0 0 wherein n is a number in the range from 1 to about 6 until the hides are tanned.

2. A process of tanning hides comprising applying to the hides a tanning composition containing as the tanning agent a glycerol polyglycide ether corresponding to the formula wherein n is a number in the range from 1 to about 6 in aqueous suspension until the hides are tanned.

3. The process of claim 2. wherein n has a value of about 2.

4. A process of tanning hides comprising applying to the hides a tanning composition containing as the tanning agent a glycerol polyglycide ether corresponding to the formula wherein n is a number in the range from 1 to about 6 until the hides are tanned and then retaining the resulting hides with a vegetable tanning agent.

5. A process of tanning hides comprising applying to the hides a tanning composition containing as the tanning agent a glycerol polyglycide ether corresponding to the formula CH243H-CHz-0[0H:CHOHCH:-O]-rCHrGH-QH,

0 wherein n is a number in the range from 1 to about 6 6 in aqueous suspension until the hides are tanned and 2,521,912 Greenlee Sept. 12, 1950 then retanning the resulting hides with a vetetable 1841- 2,688,607 Suen Sept. 7, 1954 agent FOREIGN PATENTS 833,993 Germany Mar. 13, 1952 Referen'ces Cited in the file of this patent 5 OTHER REFERENCES UNITED STATES PATENTS 2,131,145 2,512,996 Bixler June 27, 1950 Schlack Sept. 27, 1938 JSLTC, vol. 37, No. 9, September 1953, pages 302-303. 

1. A PROCESS OF TANNING HIDES COMPRISING APPLYING TO THE HIDES A TANNING COMPOSITION CONTAINING AS THE TANNING AGENT A GLYCOL POLYCLYCIDE CORRESPONDING TO THE FORMULA FIG01 WHEREIN N IS A NUMBER IN THE RANGE FROM 1 TO ABOUT 6 UNTIL THE HIDES ARE TANNED. 